Normal Stress Differences from Hole Pressure Measurements

Lodge, A. S.

doi:10.1007/978-94-017-2898-0_11

Cited by 6 publications

(8 citation statements)

References 33 publications

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“…The first normal stress difference (N,) can be calculated using the expression of Lodge (1988) where P h is the hole pressure. The first normal stress coefficient ($,I is calculated by…”

Section: Calculationsmentioning

confidence: 99%

“…A capillary rheometer can be used to generate a uniaxial extensional flow. However, the slit rheometer in addition is also capable of measuring the first normal stress difference using the hole-pressure method of Lodge (1988). The pressure difference between the flush mounted transducer and that located at the base of the slot directly opposite to it is called the hole pressure.…”

Section: Introductionmentioning

confidence: 99%

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Slit Rheometer Studies of Wheat Flour Dough1

Bhattacharya

1993

Journal of Texture Studies

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Rheological properties of bread dough having different levels of added gluten (0, 2.5, 5.0 and 7.5%) were measured. The dough was forced through a slit die attached to a cylindrical container. The material functions of interest included steady shear viscosity, first normal stress coefficient in steady shear flow derived from hole pressure measurements and planar extensional viscosity as estimated from entrance pressure drop measurements. These rheological properties were correlated to the loaf volume of the baked bread. Results indicate that the first normal stress coefficient and planar extensional viscosity were affected by the gluten content of the dough and correlated well with the loaf volume. The entrance pressure drop increased with increasing apparent shear rate but entrance correction was found to decrease with apparent shear rate. Water had a greater effect on the rheological properties than gluten content. The Trouton ratio was rather large and ranged between 850 to 2000 at a strain rate of 1s‐1 and decreased with increasing extension rate for most cases.

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“…The first normal stress difference (N,) can be calculated using the expression of Lodge (1988) where P h is the hole pressure. The first normal stress coefficient ($,I is calculated by…”

Section: Calculationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Slit Rheometer Studies of Wheat Flour Dough1

Bhattacharya

1993

Journal of Texture Studies

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“…Both N, and 7e are difficult to measure, particularly at higher deformation rates typical of extrusion like processes. However, a slit rheometer can easily be adapted for the measurement of N, (Han 1988;Lodge 1985Lodge , 1988. Similarly, qc can be obtained from the entrance pressure drop measurements made on a slit or cylindrical viscometer (Cogswell 1972;Binding 1988;Gibson 1988).…”

Section: Introductionmentioning

confidence: 99%

“…These are the exit pressure and the hole pressure methods. Both methods have been extensively evaluated for polymer melts and solutions (Han 1988;Lodge 1988). Viscoelastic fluids are known to exhibit nonzero pressure at the exit of a tube as the fluid exits into the atmosphere.…”

Section: Introductionmentioning

confidence: 99%

“…1). Lodge and co-workers (Lodge and deVargas 1983;Lodge 1985Lodge , 1988 successfully utilized this phenomenon to measure the normal stress differences for polymer solutions and melts. The original equations relating the hole pressure and the normal stress differences were derived by Higashitani and Pritchard (1972) without the assumptions of any constitutive equations.…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of the Hole Pressure Method to Measure the First Normal Stress Difference of Corn Meal Dough During Extrusion Cooking

Bhattacharya

Padmanabhan

1994

Journal of Texture Studies

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Rheological properties of food dough melt, such as steady shear viscosity (η) and first normal stress difference (N1), were measured using an in‐line slit die rheometer attached to a laboratory model single‐screw extruder. The flow rate through the rheometer was varied by altering the screw speed. Alternatively, a sidestream valve, to vary the flow rate through the rheometer at fixed screw speed, was also used to obtain rheological data. The slit die rheometer was tested with corn meal at three different experimental conditions: 25% and 35% moisture contents at 180C barrel temperature and 35% moisture content at 150C barrel temperature. N1 was measured using the hole‐pressure and exit‐pressure method. Exit pressure measurements were found to be erratic and unreliable. Hole pressure increased monotonically with increasing flow rate and was found to be affected by the processing history. The magnitude of the hole pressure ranged between 2% and 21% of pressure of the flush mounted transducer. For the experimental conditions used in this study, N1 ranged from 3 × 104 to 6 × 105 Pa for shear rates between 30 to 400 s−1. Possible sources of errors in the hole pressure measurements are discussed.

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Process rheometers for molten plastics: A survey of existing technology

Dealy

Broadhead

1993

Polymer Engineering & Sci

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There are many operations in the plastics industry where it is useful to be able to monitor the rheological properties of a melt as it is being processed. Such operations include polymerization, blending, compounding, and reactive extrusion. The design of such instruments poses major challenges, as there is a conflict between the need for rapid sample renewal and the desire for measurement accuracy. In‐line types, which are installed directly in the process flow, have a rapid response but must operate in an environment where temperature, pressure, and flow rate fluctuate in response to process upsets. On‐line types, which make use of a side stream and gear pump to feed the rheometer, allow for more freedom in the design of the rheometer but have an inherent signal delay due to the time required for melt to reach the rheometer. A variety of rheological sensors have been described in the patent and research literature, each with its unique advantages and disadvantages, and some of these are finding increased use in the plastics industry to improve product quality and process efficiency.

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Normal Stress Differences from Hole Pressure Measurements

Cited by 6 publications

References 33 publications

Slit Rheometer Studies of Wheat Flour Dough1

Slit Rheometer Studies of Wheat Flour Dough1

Evaluation of the Hole Pressure Method to Measure the First Normal Stress Difference of Corn Meal Dough During Extrusion Cooking

Process rheometers for molten plastics: A survey of existing technology

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